Automatic analyzers are used to measure the properties of analytes (e.g., biological samples, such as blood serum and urine, or analyte-reagent mixtures), thereby performing analysis of the analytes.
Such an automatic analyzer typically uses a probe to suction an analyte (or an analyte-reagent mixture) so that the analyte can be transferred to its analyzer unit. In such a case, it is necessary to immerse the lower end of the probe as shallowly into the analyte as possible, so as to prevent the analyte from being attached to the outer surface of the probe and then mixed with another analyte (in other words, to prevent cross-contamination). For this reason, what is needed is detection of the liquid surface level of the analyte relative to the probe.
A known conventional liquid-surface detection technique involves the use of a probe both as an electrode and as an electrically active component. The probe is used for the detection of the capacitance between the probe and a grounded reaction vessel (i.e., the analyte therein, which is also grounded), and monitoring changes in the capacitance allows detection of the liquid surface level of the analyte relative to the probe (see Patent Document 1).